Solutions have already been proposed to make the interface formed by the electrodes arranged between a display and an observer remain as discreet as possible and to avoid damaging the aesthetic appearance of the electronic apparatus, particularly in the case of a timepiece. For example, wristwatches are known in which the inner face of the glass includes electrodes allowing tactile control of the time or non time-related functions by capacitive or resistive effect, as is disclosed in a non-limiting manner in U.S. Pat. No. 4,228,534 and EP Patent Nos. 0 674 247 and 1 207 439. The glass can also be replaced or completed by a cell formed of two substrates with transparent electrodes between which an active material is placed, for example to form a photovoltaic cell forming the energy source as described in WO Patent No. 93/19479, or to form a liquid crystal cell able to have a transparent state or a state for displaying complementary or different data to that displayed on a subjacent dial, as described in WO Patent No. 99/32945.
In order to make the electrodes transparent conductor oxides (TCO) are used in a known manner, i.e. materials which are both good conductors and transparent in the visible field, such as tin and indium oxide (ITO), In2O3 or SnO2 doped with antimony. Transparent conductive polymer, which are organic components with conjugated double bonds whose conductivity can be improved by chemical or electrochemical doping, can also be used as a conductive film for structuring the electrodes. It may be, for example a polyacetylene or polyanilines such as Ormecon®. These films, of the order of 50 to 100 nm, are carried out directly onto the transparent substrate or onto an intermediate layer via a large number of known techniques, such as sputtering, evaporation, the sol-gel technique, and chemical vapour deposition (CDV), from which laser assisted chemical vapour deposition should be noted (LICVD).
As regards the structure of the electrodes, there also exist various known methods implemented by using at least one mask corresponding to the contour of the electrodes, either during the deposition of the TCO by localised crystallisation of a sol-gel film by UV laser irradiation, or by carrying out, on a continuous TCO film, a chemical etch or localised ablation by UV laser irradiation with sufficient fluence. The nature of the transparent substrate, glass or plastic is evidently a determining factor, from the technical and economical point of view, for the choice of process to be applied. Localised crystallisation of a sol-gel film by UV laser is hardly, for example, applicable to a plastic substrate, such as PMMA, since it is a photothermal process.
Moreover, the use of very aggressive chemical components in the selective etching methods can lead to degradation of the substrate or of an intermediate layer inserted between said substrate and the TCO film, such that the non-conductive spaces between the electrodes can still remain perceptible to the naked eye whatever the method used for filling the non-conductive spaces these non-conductive spaces can also be visible because of the difficulty in filling them without forming bulges or depressions capable of deviating the light rays, given that it is necessary to use two complementary masks, respectively for etching and for filling.
In order to overcome the aforementioned drawback, the method proposed in European Patent Application No. 03005615.4 (published as EP 1 457 865 A1) and in U.S. Pat. No. 7,449,732 B2, both of which are in the name of the Applicant, incorporated herein by reference, consists in using a single mask employing a laser radiation whose features (fluence, number of impulses, frequency) are adjusted in accordance with two different modes for two successive steps. The first step consists in totally eliminating the TCO in the non-conductive spaces, and the second step in causing deposition of a material having a suitable refractive index and thickness in said spaces. It seemed in fact quite obvious that two electrodes close to each other could only be electrically insulated by removing any trace of conductive material in the space separating them.